import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class BinaryTree {

    static class TreeNode {
        public char val;
        public TreeNode left;//左孩子的引用
        public TreeNode right;//右孩子的引用

        public TreeNode(char val) {
            this.val = val;
        }
    }


    /**
     * 创建一棵二叉树 返回这棵树的根节点
     *
     * @return
     */
    public TreeNode createTree() {
        TreeNode A = new TreeNode('A');
        TreeNode B = new TreeNode('B');
        TreeNode C = new TreeNode('C');
        TreeNode D = new TreeNode('D');
        TreeNode E = new TreeNode('E');
        TreeNode F = new TreeNode('F');
        TreeNode G = new TreeNode('G');
        TreeNode H = new TreeNode('H');
        TreeNode I = new TreeNode('I');
        //
        A.left = C;
        A.right = B;
        C.left = D;
        D.left = G;
        D.right = H;
        B.left = E;
        B.right = F;
        E.left = I;
        return A;
    }

    // 前序遍历 A C D G H B E I F
    public void preOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        System.out.print(root.val + " ");
        preOrder(root.left);
        preOrder(root.right);
    }

    // 中序遍历 G D H C A I E B F
    void inOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        inOrder(root.left);
        System.out.print(root.val + " ");
        inOrder(root.right);
    }

    // 后序遍历 G H D C I E F B A
    void postOrder(TreeNode root) {
        if (root == null) {
            return;
        }
        postOrder(root.left);
        postOrder(root.right);
        System.out.print(root.val + " ");
    }

    public static int nodeSize;

    /**
     * 获取树中节点的个数：遍历思路
     */
    public void size(TreeNode root) {
        if (root == null) {
            return;
        }
        nodeSize++;
        size(root.left);
        size(root.right);

    }

    /**
     * 获取节点的个数：子问题的思路
     *
     * @param root
     * @return
     */
    public int size2(TreeNode root) {
        if (root == null) {
            return 0;
        }

        //结点个数 = 左子树的结点 + 右子树的结点 + 1
        return size2(root.right) + size2(root.left) + 1;

    }


    /*
     获取叶子节点的个数：遍历思路
     */
    public static int leafSize = 0;

    public void getLeafNodeCount1(TreeNode root) {
        if (root == null) {
            return;
        }
        if (root.left == null && root.right == null) {
            leafSize++;
        }
        getLeafNodeCount1(root.left);
        getLeafNodeCount1(root.right);
    }

    /*
     获取叶子节点的个数：子问题
     */
    public int getLeafNodeCount2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        if (root.left == null && root.right == null) {
            return 1;
        }
        return getLeafNodeCount2(root.left) + getLeafNodeCount2(root.right);
    }

    /*
    获取第K层节点的个数
     */
    public int getKLevelNodeCount(TreeNode root, int k) {
        if (root == null) {
            return 0;
        }
        if (k == 1) {
            return 1;
        }
        return getKLevelNodeCount(root.left, k - 1) +
                getKLevelNodeCount(root.right, k - 1);
    }

    /*
     获取二叉树的高度
     时间复杂度：O(N)
     */
    public int getHeight(TreeNode root) {
        if (root == null) {
            return 0;
        }
/*        int leftHeight = getHeight(root.left);
        int rightHeight = getHeight(root.right);
        return Math.max(leftHeight, rightHeight) + 1;*/
        return Math.max(getHeight(root.left), getHeight(root.right)) + 1;
    }


    // 检测值为value的元素是否存在
    public TreeNode find(TreeNode root, char val) {
        if (root == null) {
            return null;
        }
        if (root.val == val) {
            return root;
        }

        //
        TreeNode ret = find(root.left, val);
        if (ret != null) {
            return ret;
        }

        ret = find(root.right, val);
        return ret;
    }

    //层序遍历
    public List<Character> levelOrder(TreeNode root) {
        // 初始化队列，加入根节点
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        // 初始化一个列表，用于保存遍历序列
        List<Character> list = new ArrayList<>();
        while (!queue.isEmpty()) {
            TreeNode node = queue.poll(); // 队列出队
            list.add(node.val); // 保存节点值
            if (node.left != null) {
                queue.offer(node.left); // 左子节点入队
            }
            if (node.right != null) {
                queue.offer(node.right); // 右子节点入队
            }
        }
        return list;
    }


    // 判断一棵树是不是完全二叉树
    public boolean isCompleteTree(TreeNode root) {
        return true;
    }
}